A paper-making step in a paper-making machine generally has a wire part in which a dispersion of pulp in water is placed on a net (wire) for paper-making and excess water is allowed to drop naturally, to obtain a wet paper, a press part in which the wet paper is passed between a pair of press rolls and pressed by the press rolls via felt, thereby transferring water in the wet paper into the felt, to dehydrate the wet paper, a dry part in which the wet paper passed through the press part is dried by contacting with a cylinder heated, to give a paper, and a reel part in which the paper is wound on a rod called spool.
The dry part has apparatuses such as a cylinder for heating and drying the wet paper, a canvas for pressing the wet paper to the cylinder, a canvas roll for guiding the canvas, a calender roll for controlling the thickness and the smoothness of the wet paper dried, a breaker stack roll for mildly controlling the thickness and the smoothness of the wet paper dried, and has a problem that pitch adheres to the surfaces thereof. When pitch adheres to them, the paper is contaminated, causing a significant lowering in its yield.
In contrast, a silicone-based contamination inhibitor composition is known as a contamination inhibitor composition which can inhibit pitch contamination by imparting to a dry part.
As the silicone-based contamination inhibitor composition, for example, a contamination inhibitor composition containing a polysiloxane compound having a prescribed chemical structural formula in which the number of amino-modified groups per molecule of the polysiloxane compound is 0.5 to 5 is known (see, e.g., PTL 1).
With the above-described contamination inhibitor composition, however, the region wherein pitch contamination can be inhibited is limited to a site to which the contamination inhibitor composition is imparted in the dry part. Accordingly, it is necessary to impart the contamination inhibitor composition at several positions on the dry part.
For this purpose, a contamination inhibitor composition is known containing a low molecular polysiloxane compound having a prescribed chemical structural formula and a high molecular polysiloxane compound having a prescribed chemical structural formula in which the kinetic viscosity at 25° C. of the low molecular polysiloxane compound is 10 to 300 mm2/s and the kinetic viscosity at 25° C. of the high molecular polysiloxane compound is 40 to 90000 mm2/s, the number of modified groups per molecule of the low molecular polysiloxane compound is 0.1 to 3.0 and the number of modified groups per molecule of the high molecular polysiloxane compound is 1.0 to 10, and the number m of repetition of the polysiloxane unit in the low molecular polysiloxane compound and the number n of repetition of the polysiloxane unit in the high molecular polysiloxane compound satisfy the relation of:2m≤n(see, e.g., PTL 2).
With the contamination inhibitor composition described above, the high molecular polysiloxane compound forms a film on the dry part to which the contamination inhibitor composition has been imparted, meanwhile the low molecular polysiloxane compound transfers to a wet paper and is conveyed by the wet paper, and is re-transferred to the dry part at the downstream side toward which the wet paper is guided, thus, the contamination inhibitor composition is imparted over a wide range of the dry part and pitch contamination can be inhibited effectively.